Implementation and Evaluation of P.880 Methodology

Abstract: Continuous Evaluation of Time Varying Speech Quality (CETVSQ) is a method of subjective assessment of transmitted speech quality for long speech sequences containing quality fluctuations in time. This method is modeled for continuous evaluation of long speech sequences based on two subjective tasks. First task is to assess the speech quality during the listening and second task is to assess the overall speech quality after listening to the speech sequences. The development of continuous evaluation of time varying speech quality was motivated by fact that speech quality degradations are often not constant and varies in time. In modern IP telephony and wireless networks, speech quality varies due to specific impairments such as packet loss, echo, handover in networks etc. Many other standard methods already exist, which are being used for subjective assessment of short speech sequences. These methods such as ITU-T Rec. P.800 are well suited for only time constant speech quality. In this thesis work, it was required to implement CETVSQ methodology, so that it could be possible to assess long speech sequences. An analog hardware slider is used for the continuous assessment of speech qualities, as well as for overall quality judgments. Instantaneous and overall quality judgments are being saved into Excel file. The results stored in the Excel file are analyzed by applying different statistical measures. In evaluation part of the thesis work, subjects’ scores are analyzed by applying statistical methods to identify several factors that have originated in the CETVSQ methodology. A subjective test had already been conducted according to P.800 ACR method. The long speech sequences were divided into 8 seconds short sequences and then assessed using P.800 ACR method. In this study, the long speech sequences are assessed using CETVSQ methodology and comparison is conducted between P.800 ACR and CETVSQ results. It has been revealed that if long speech sequences are divided into short segments and evaluated using P.800 ACR, then P.800 ACR results will be different from the results obtained from CETVSQ methodology. The necessity of CETVSQ methodology is proved by this study.